SE518041C2 - Method for sensing the amount of filling in a tank system - Google Patents

Abstract

The invention is directed to a method for detecting a fill level of a tank system utilizing a pressure source, a bridge divider arrangement and a pressure measuring device. The pressure source is adapted to generate a change of pressure in the tank system. The pressure divider arrangement has a reference measuring unit which can be charged with pressure by the pressure source. The reference measuring unit further includes at least one flow resistor of a predetermined size in at least one reference flow branch. For measuring the tightness, the pressure measuring device simultaneously detects the difference of the pressure in the tank system and of the pressure in the reference measuring unit. In the method, the time-dependent trace of the difference pressure during at least one of a pressure build-up operation and a pressure decay operation is continuously detected. A conclusion is then drawn as to the fill level from the time-dependent trace.

Description

20 »: 'i25 nns,.

II) I,. ''30. 518 041 v. As a result of differences. On the other hand, the method requires a technically relatively complicated construction with a number of sensors and test devices.

The invention is therefore based on the task of further developing a method for tightness testing of a tank system of the type mentioned in the introduction so that if possible without additional sensors, sensors and the like and therefore cost-effective a very precise information can be given about the degree of filling of a liquid in the tank system. .

Advantages of the invention.

In a method for sensing the amount of filling of a tank system in accordance with what is initially described, this object according to the invention is solved in that the method has the characteristics indicated in claim 1.

The continuous sensing of the time course of the differential pressure during the pressure increase and / or pressure reduction course and the conclusion drawn from this time course regarding the degree of filling has the special great advantage that a leak test of the tank system is easily and without additional sensors, sensors and the like possible. a device for testing the tightness of the tank system.

In principle, a single flow resistor in a pressure gauge is sufficient to detect a leak and to determine the amount of filling in a tank system.

A particularly advantageous embodiment of the method is stated in claim 2.

The design of the pressure divider arrangement as a pressure divider bridge with a differential pressure gauge arranged in the bridge diagonal has in particular the great advantage that in the event of a leak to be shielded, the device is balanced and thus in this operating point independent of tolerances of the pressure source. This enables a very accurate determination of the filling amount in the tank system. In addition, the gasification from a liquid present in the tank system can be determined in a simple manner. 10 15 20 25 riff) 518 041 3 It is also advantageous that the method for determining the filling quantity in a tank system by means of a differential pressure measurement is independent of the ambient pressure around the tank system.

The flow resistors are preferably dimensioned so that they have the same magnitude as the flow resistance of a minimum leakage intended for diagnosis of the tank system. However, it is also possible that the flow resistors have different sizes.

A very advantageous embodiment of the method is stated in claim 4.

By comparing the time course of the differential pressure increase event with the time course of the differential pressure increase event, a falsification of the degree of filling, which is caused by a gasification of the liquid present in the tank system, which is practically unavoidable, is especially avoided.

Another advantageous embodiment of the method is stated in claim 5. This method allows, by the rapid inflation of the tank system, in a particularly advantageous manner a rapid determination of the filling amount of the tank system.

An embodiment of the process specified in claim 6 is suitable for eliminating the gasification of a liquid which is essential in the tank system.

Another particularly advantageous embodiment of the method is stated in claim 7.

Drawing.

Additional features and advantages of the invention are described in more detail below with the aid of some embodiments with reference to the accompanying drawings. 10 15 20 “Å fi» vara i in; i .. - -30 I n in i 518 041 H On these shows: fi g. 1 a device for leak testing of a motor vehicle tank system, which is used to carry out the method according to the invention for filling degree determination, _ fi g. 2a and 2b schematically show the pressure course over time in a motor vehicle tank system during a pressure increase resp. during a pressure drop, and fi g. 3 shows a device known from the prior art for determining the filling quantity of a motor vehicle.

Description of the embodiments.

The method for decelerating the filling quantity of a tank system is described below by means of a motor vehicle tank system. However, the method is not limited to a motor vehicle tank system but can in principle be used in arbitrary tank systems.

As shown in fi g. 3, a filling gradient known from the prior art of a motor vehicle rich system has an tttouter 11 arranged in a tank 10, which is connected to a potentiometer 20. Depending on the position of the fltouter 11, an electrical signal is generated in the potentiometer 20, which is a direct measure of the filling level in tanks 10.

In the method described below for determining the filling quantity of a motor vehicle tank system, no such filling gradient is required.

A motor vehicle tank system comprises a tank 10, which is connected via an activated carbon filter 12 and a tank vent valve 14 to an intake pipe 20 of an internal combustion engine (not shown). A damper 22 is arranged in the suction pipe 20.

By evaporation, 10 hydrocarbon gases are generated in the tank, which accumulate in the activated carbon filter 12.

To regenerate the activated carbon filter 12, the tank vent valve 14 is opened, so that due to the negative pressure prevailing in the intake pipe 20, air is sucked from the atmosphere through the active carbon filter 12, whereby the hydrocarbons accumulated in the active carbon filter 12 are sucked into the intake pipe 20 and the intake pipe. 10 15 20 .___: 30 518 p 041 To test the tightness of the motor vehicle tank system, there is a pump 30, which is connected to the motor vehicle main system via a pressure divider bridge 40.

The pressure divider bridge 40 comprises a building branch 41, in which two flow resistors 42, 43 are arranged between the pump 30 and the atmosphere. .

The flow resistors 42, 43 and 47 are then dimensioned as the flow resistance of a minimum leakage intended for diagnosis of the tank system. A differential pressure gauge 50 is arranged in the bridge diagonal.

Before the actual degree of filling is determined, a leak diagnosis is now carried out to begin with.

For leakage diagnosis, a pressure is initially generated by the pump 30 in the entire motor vehicle tank system. If there is no leakage, a differential pressure Apa fi0 occurs at the differential pressure gauge 50, which indicates the absence of a leakage. If, on the other hand, a leak is present and has a magnitude corresponding to the flow resistances 42, 43, 47, the pressure divider bridge is "balanced", so that no differential pressure (Ap = 0) is shielded by the differential pressure gauge 50 and the presence of a leak is indicated in this way.

In the absence of leakage, the degree of filling of the tank system is then carried out in the manner described below.

The shut-off valve 61, which is arranged as a bypass pipe to the accidental bridge 40, is closed. By means of the pressure source, the tank system is pressurized via the flow resistor 47. 10 15 20 ÜÛß 111; .n-> n I a os: nn 518 041 6 Thereby the pressure p1 in one branch of the pressure divider bridge 40 initially starts immediately to half the pump supply pressure, since the flow resistor 42 is the same size as the flow resistor 43. The pressure p2 in the other branch of the pressure divider bridge 40 rises by a time constant to the pump feed pressure, the time constant being dependent on the flow resistance 47 and the flow resistance of the entire tank system. From the time course of the sensed diameter pressure, it is possible to calculate the free tank volume and thus the degree of filling.

The pressure profile of the pressure p2 in the branch 46 then shows that in fi g. 2a illustrated the process.

The gasification of the fuel present in the motor vehicle tank system occurs as the largest quantity. This gasification causes a further increase in pressure in the tank system and therefore gives the appearance of a fuller tank. The pressure course with dry-present pre-gasification is illustrated in Fig. 2a schematically by means of a broken line. In order to eliminate the gasification, in addition to the pressure increase event, the pressure drop event is also evaluated in the following manner.

The pressure source 30 is switched off after a consequent pressure increase. The shut-off valve 61 and the tank vent valve 14 are closed. The overpressure in the tank system is lowered only via the flow resistor 47 and the very large flow area of the pressure source 30 in comparison with the flow paths of the pressure divider bridge 40, the pressure p1 then immediately assumes the ambient pressure. The pressure p2, on the other hand, drops by a time constant, which depends on the flow resistance 47 and the flow resistance of the entire tank system, to the ambient pressure. From the time course of the diurnal junk cigarette, the free tank volume and thus the degree of filling can be calculated. Such a pressure sequence is shown in fi g. 2b.

As also shown in fi g. 2b, however, the dry gasification of a liquid present in the tank system delays the pressure drop (dashed line) and therefore gives the appearance of a larger fi in tank volume (empty tank). efavv 10 15 20 518 041 1- By comparing the two pressure processes during inflation (pressure increase) and during pressure reduction, the gasification can now be compensated so that the degree of filling appears as a residual quantity.

This degree of filling can be repeated in each basic adaptation phase, ie. in the case of inactive tank venting, whereby statistics are allowed and the regeneration speed of the active carbon filter 12 is not limited. However, such a process requires a low tolerance pressure source. In order to be able to use an arbitrary pressure source, especially one which does not show any such small tolerances, the degree of filling can alternatively be carried out in the following manner.

First, the bypass pipe valve 61 is opened and the pressure source is switched on. This causes a rapid increase in pressure in the tank system. After a predetermined time, the bypass valve 61 is closed and the pressure source 30 is disconnected. The pressure now prevailing in the tank system drops via the flow resistance 47. The continuously measured time-dependent pressure course is a measure of the degree of tank filling.

In this case, the desired tank volume applies: t VT = (Rsp-TT / (Pfü) -Pol lm (f) df 0 Where the mass flow via the scattering equation: m = a -A -pn / z / (R fr) -Jz / <1 - 1) w / (pa / prf / f - ”f 10 15, .f. = 20 5-18 041 0 0 In these equations means: VT tank volume, TT tank temperature, pf tank pressure, take ambient temperature, pa ambient key, m den outflowing mass flow, a the orifice number for the flow resistance of the tank system, A the area of the flow resistance of the tank system, X the isentropic exponent, Rsp special gas constants, p0 the starting pressure at the beginning of the measurement.

The advantage of this measuring method is a measurement independent of the feed effect of the key source 30, since the measurement takes place at a disconnected pressure source 30. In addition, a rapid pressure increase is guaranteed through the opened bypass valve 61, whereby the degree of filling can be carried out in a short time.

One problem, however, is that the gasification of a liquid present in the tank system falsifies the measurement in such a way that it reflects a fuller tank. : wars 10 15 20 anü 518 Û41 “l To take this gasification into account, the gasification can on the one hand be estimated via the charging of the activated carbon 12, whereby the degree of filling degree is either corrected or suppressed at high gasification. On the other hand, the gasification can also be measured by means of the differential pressure sensor 50. For this purpose, a special measuring method is performed, in the first stage of which the tank vent valve 14 is closed to eliminate the differential pressure sensor oil, while the bypass valve 61 is opened. The dilier pressure measured thereby is interpreted as sensor offset and a balancing of the differential pressure sensor takes place. In a second step, a degree of filling is carried out as described above, the result of which is falsified by a possible gasification. In a third step, the gasification rate is monitored by evaluating the final pressure difference, which the differential pressure sensor 50 detects at the degree of filling network. This final pressure difference is a measure of the gasification. Namely, the larger the dry gasification, the higher the pressure drop at the flow resistor 47 and the higher the pressure p2 measured in the flow branch 46. The final pressure difference is thus a measure of the fuel gasification (pgas in fi g. 2b). With this value, the above degree of filling degree network can now be conjugated.

The advantage of this determination of the gasification lies in the fact that the degree of filling is independent of the sensor offset and independent of pump tolerances.

The degree of filling can be carried out in each basic adaptation phase, ie. in the case of inactive tank venting, whereby on the one hand statistics are made possible and on the other hand no restriction occurs on the regeneration speed of the activated carbon filter 12. ivat. 10 518 * 041 IO Since all the procedures described above are affected by any existing leakage, - as already mentioned above - a leakage measurement must always first be carried out in order to either correct or reject the degree of filling result. For this reason, the device for determining the density of a tank system can be combined in a particularly advantageous manner with filling degree measurement in the manner described above.

The advantage of the method described above is the continuous sensing of the pressure process, which allows precise determination of the degree of filling of the tank. This continuous sensing of the temporal pressure course allows in particular more precise degree of filling determinations than in known gradient measurements, in which the whimsy course is always obtained over a period of time, and in which the changing pressure course cannot be shielded within the period of time.

Claims (7)

10 15 20: apan 25 51 8 0 4 1 \\ Patentkrav A method for sensing the filling amount of a tank system by means of a pressure source, by means of which a pressure change can be generated in the tank system, a pressure divider device with a reference measuring device, comprising at least one flow resistor of predetermined size in at least one reference pipe clearance branch. the source can be loaded with pressure, and a pressure measuring device, by means of which for tightness testing the difference between the pressure in the tank system and the pressure in the reference measuring device is simultaneously shielded, characterized in that the time course of the differential pressure is continuously shielded during the pressure rise and / or pressure drop cycle. derived from this time course. Method according to claim 1, characterized in that the die pressure is shielded by means of a differential pressure grid arranged in the bridge diagonal of a pressure divider bridge, one branch of the bridge comprising two scattering resistors arranged between the pressure source and the atmosphere, the other branch of which tank system, the tightness of which is to be examined, and an additional flow resistor arranged between it and the pressure source. Method according to Claim 2, characterized in that the flow resistors are selected so that they have the same magnitude as the flow resistance of a minimum leakage intended for diagnosis. Method according to one of the preceding claims, characterized in that the time course of the pressure difference during the pressure rise disturbance is first continuously sensed, that the time course of the pressure difference during the pressure drop course is sensed continuously, and that the degree of filling of these tanks is derived from the comparison between time course. Method according to one of Claims 1 to 3, characterized in that a pressure in the tank system is initially built up via a bypass valve, that the bypass valve and the pressure source fi are then connected and that the degree of filling is derived from the sensed time course of the differential pressure. Method according to Claim 5, characterized in that the gasification of a liquid present in the tank system is mathematically estimated and used to correct the differential pressure profile. Method according to claim 5, characterized in that for measuring the gasification of a liquid present in the tank system, in a special measuring method, the measured diurnal pressure is interpreted as offset when the bypass valve and sealed tank system are opened, then the time course of the pressure in the tank system and in the reference measuring device is continuously sensed while the tank system is loaded with pressure, and that the differential pressure thus obtained is used for correcting the gasification.